Electric air circuit breaker



NOV. 28, 1944. M. BENNETT 2,363,853

ELECTRIC AIR CIRCUIT BREAKER Filed June 5, 1942 ABC GAS VENT lnventpfz 'Robert Bennett,

, His Attorney.

Patented Nov. 1944 2,363,853 ELECTRIC AIR cmculr BREAKER Robert M. Bennett, Ithan, Pa", assignor to General Electric Company, a co poratlon of New York Application June 5, 1942, Serial No. 445,857

4 Claims.

My invention relates to electric air circuit breakers, more particularly to air circuit breakers for interrupting moderate voltage power circuits under all current interrupting conditions including the interruption of both low amperage and short circuit current arcs.

The interruption of high amperage moderate voltage power arcs by air circuit breakers of the magnetic blowout type rated at from 5000 to 7500 volts for example, has been successfully accomplished and such circuit breakers have been putinto extensive commercial use. These breakers can also be made to interrupt light currents at 15 kv. but at heavier currents are less satisfactory. Although various methods have been proposed for enabling the circuit breaker to interrupt both high and low current arcs,

such as for example applying an auxiliary fluid jet for interrupting arcs in the low current range, the problem of interrupting such low amperage arcs within a cycle or two of arcing presents itself from the practical standpoint whenever a new design of high current interrupting capacity breaker is developed. This is due to the fact that the circuit breaker characteristics favoring the interruption of high or short circuit current arcs do not always favor the interruption of low current arcs, so that a low current are may hang on for an excessively long arcing time before it is finally extinguished.

A principal object of my invention therefore is the provision of an improved air circuit breaker that is capable of efiiciently interrupting large overload and short circuit currents as well'as extinguishing low amperage arcs and arcs of intermediate current values, all within a very brief arcing time.

In accordance with my invention, radically different circuit breaker characteristics are combined in such a manner that an effective and efficient arc extinguishing agency is applied for interrupting the power arc regardless of its current magnitude. I accomplish this by using a resistance method of arc interruption wherein the arc is greatly lengthened and attenuated as it is forced into contact with cooling surfaces of large area, and a so-called expulsion method wherein interrupting gas is liberated by the are heat from insulating structure closely adjacent or in confining relation to the arc and caused to flow through the arc stream. The volume of such gas liberated is proportional to the magnitude of the arc current.

My invention will be more fully set forth in the following description 4 referring to the accomcubicle (not shown).

panying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing, Fig. 1 is an elevational 'view, partly in section of an air circuit breaker of the double-break type embodying my invention and Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.

The air circuit breaker illustrated by Fig. 1 is shown for example in a form that is particularly adaptable for central stations and substations wherein the circuit breaker unit can be bodily connected and disconnected with respect to the stationary circuits by a simple plugging operation. In the present instance, the circuit breaker is of the well-known drop-down type wherein disconnection is effected merely by bodily lowering of the circuit breaker after the breaker has been opened. The breaker unit, including its supporting frame indicated at l is usually housed in a grounded metal enclosure or The relatively movable contact structure of the breaker comprises a pair of fixed contacts at 2 and 3 and a relatively movable coacting bridging contact 4 that is operatedby means of a reciprocally movable insulating rod 5. The operating rod 5 is suitably connected to an actuating mechanism (not shown) carried by the frame 1 so that upon lowering of the bridging contact two breaks in series are formed in the power circuit. The fixed contacts 2 and 3 are electrically connected to the lower ends of the lead-in conductor studs 6 and 1 respectively which also serve as plug type disconnecting contacts for the breaker unit. When the breaker is connected in a power circuit, lowering of the bridge contacts 4 to open the circuit may cause an arc to form at each break. It will be apparent that the two series breaks may be formed either simultaneously or in timed sequence as desired.

In order to extinguish the arcs so formed at the series breaks 24 and 3-4 under all arcing conditions including low and very high amperage arcs, I provide at the break 2--4 an arc chute 8 of the interference-barrier type for example, and at the break 3-4 an arc chute 9 of the expulsion type. The arc drawnat the arc chute 8 is subjected to intensive cooling and attenuation so that the resistance of the arc stream is greatly increased, and the arc at the chute 9 is subjected to the expulsion effect of suddenly liberated arc-extinguishing gas, the amount of the gas liberated depending on the are heat' and consequently the arc current magnitude. By subjecting the two portions of the interrupting arc to these fundamentally different arc extinguishing methods, I provide means for always applying, at least to one arc, an eflicient and positive arc extinguishing agency regardless of the magnitude of the arc current.

The arc extinguishing structure generally indicated at 8 is mounted with respect to the separable contacts at 2-4 so as directly to receive the power arc which is under the influence of a magnetic blowout force, such as produced by blowout coils l and H in a manner similar to the conventional arc chute wherein the arc is formed at the entrance of the chute and is rapidly extended in the form of a loop through the chute toward the exhaust opening at the opposite end thereof. Certain features of this extinguishing structure are disclosed and claimed in Letters Patent No. 2,293,513, issued August 18, 1942 to L. J. Linde.

Referring now to both Figs. 1 and 2, the arc chute 8 comprises spaced side walls l2 and I3 composed of arc resisting material, preferably of inorganic insulating material such as an asbestos compound, each side wall having on the side facing the other wall a plurality of parallel ridges or fins l2 and I3 respectively. The fins I2 and I3 extend longitudinally from the chute entrance to the chute exhaust and are preferably integral with the side walls which are joined and suitably clamped together at the ends 14 and I5 so as to form an arc chute. The length and spacing of the fins l2 and I3 are preferably such that when the side walls I! and I3 are clamped together, the fins of one wall are staggered or interleaved with respect to those of the other, so

as to form a restricted sinuous or tortuous pas-- sage l6 into which the arc is driven at the entrance ll of the arc chute. As shown by Fig. 1 which illustrates in partial detail but half the extinguishing structure, namely the inner side wall 12, the fins project inwardly in a direction transverse to the direction of the movement of the arc as it passes from the entrance I'I into and through the chute. At the exhaust end of the chute suitable gas cooling structure I1 is disposed.

As the arc is driven by the magnetic blowout field into the entrance passage ll, there is comparatively little transverse deflection of the arc stream during this initial movement due to the fact that the fins l2 and N are tapered toward the arc entrance. As the arc is driven into the zigzag space defined by the interleaving fins, the cross-section of the arc is reduced as the arc assumes a serpentine form. If the arc is not interrupted in this region, the blowout field continues to move the arc outward through the are passage toward the exhaust thereby progressively lengthening the path of the arc as the amplitude of the zigzag path becomes greater. The are is thereby greatly lengthened and attenuated concurrent with great cooling effect due to the large cooling surface of the fins engaged by the arc during its approach to the exhaust arc of the chute. This cooling of the lengthened andattenuated arc stream so increases its electrical resistance that the arc current is correspondingly reduced together with improvement of the power factor. Accordingly, the interrupting operation at a current zero is greatly facilitated and is not accompanied by system disturbance.

to the arc runners I0 so that the arc current serially traverses the blowout coils after separation of the contacts in a manner well-known in the art. Normally the current is carried in the closed circuit position of the breaker by the spring-biased contact 2a which engages the contact portion 4a of the bridge, the current being shunted first to the transfer contacts 2b and 4b and then to the arcing contacts 20 and 40 as the breaker opens. After the arc is drawn at the break 2-4 and when it reaches an extended position its lower root transfers to the arc runner l I, so that the blowout coil I I, one terminal of which is electrically connected through the flexible conductor l8 to the bridge 4 and the other to the runner II, also is connected in series in the interrupting circuit. Accordingly, as the arc proceeds into the chute all the blowout coils become energized by the arc current to establish a magnetic blowout field which passes transversely across the chute between the usual pole plates (not shown) and drives the arc towards the chute exhaust according to well-known principles.

When very low values of current are to be interrupted the magnetic forces generated by the blowout coils are insufficient rapidly to move the arc through the arc passages toward the exhaust end. For this purpose a puffer comprising a cylinder 4d and a piston 46 is provided. The piston is suitably connected to the bridging contact 4 by the hollow piston rod 4; which also serves as a nozzle for directing a jet of air across the arc. Opening movement of the bridging contact 4 drives the piston 46 down in the cylinder 4d thereby forcing the air trapped below the piston to flow out through the tube 4; across the arcing contacts in a direction to drive the arc into the arc passages.

This type of arc extinguishing device is very efiective in interrupting low or moderate amperage arcs. Such arcs are not excessively fat and therefore can be driven by the blowout field into the restricted passage formed by the closely spaced interleaving fins or barriers. Also the magnetic blowout field is not so great that the arc is driven through the chute before it has had sufficient cooling contact with the chute passage walls. Within this passage the arc is greatly lengthened and squeezed between the chute side walls thereby facilitating heat transfer from the arc stream so that the arc current is rapidly decreased by the increased resistance of the arc stream. This greatly reduced arc current, together with a power factor approaching unity makes final extinction of the arc at a current zero comparatively simple.

The are chute 9 at the break 3-4 is of the expulsion type and is particularly adapted to handle considerably higher amperage arcs. The arc is formed between the finger contacts 3' secured to the fixed contact 3 and a blade-like member 4' connected to one end of the bridge 4 so that when the bridge is lowered an arc is formed in a slotlike passage I9 formed at the entrance part of the chute 9. The chute 9 comprises a pair of spaced insulating side walls composed of fiber or the like, one of which is indicated at 20, and cooperating end walls Zl and 22 of similar material arranged to form a narrow diverging arc chute, the exhaust end of which communicates with an are gas' venting conduit 22. A plurality of insulatin barriers 23 form partitions in the chute so that arcgases formed in the passage l9 fiow to the venting tube 22' through. separate passages 23'. The converging edges of the barriers 23 are spaced adjacent to the contact blade 4.so that the power are is drawn across the openings of the exhaust passages 23' in succession. Metallic cooling plates 24 are interposed in the passages 23 for reducing the temperature of the exhaust gases. The insulating barrier 25 extends across the passage l9 and is provided with a slot in registry with the blade!- for confining the arc flame within the chute at the movable contact.

For the purpose of interrupting the are formed within the passage I9, the insulating barriers 23, particularly at their converging edges, as well as the side walls of the passage I9, are composed of a material, preferably an organic material such as sage in part closely confining a portion of said interrupting arc, said passage having walls and confining structure composed of organic insulating material, such as hard fibre, adapted to release an arcextinguishing gas under influence of 'arc chute having magnetic blow-out means and hard fibre or urea resin, that is capable of pr0-- ducing under influen'ceof the are heat an appreciable volume of arc extinguishing gas. The quantity of gas liberated depends upon the intensity of the are heat at the insulating surface of the barriers and side walls, and in the case of large short circuit currents a considerable amount of interrupting gas is liberated so suddenly as to produce an explosive-like force tending to blow out the arc. This'explosive-like force tends to expel the are into the arc chute where it is stretched between the converging edges of the barrier 23 and extinguished. My invention, it should be noted, is not limited to a specific form of expulsion-type breaker at 9 and comprehends any suitable type wherein the production of arc extinguishing gas is increased in accordance with arc current values. Y

It will therefore be apparent that I have provided av double-break air circuit breaker with means for i'nterruptingmoderate voltage power currents within a wide range of interrupting conditions. Although I have shown by way of example a double-break circuit breaker, it shall be understood that it is within the scope of my invention to employ a single-break breaker wherein the arc is drawn, for example, first through the expulsion chute 9,and then through the resistance chute- 8 for finally interrupting low amperage.

arcs that are not extinguished by expulsion action within the chute 9. Also, the bridge contact 4 may readily be designed so that any desired sequence of contact separation canbe obtained.

It should be understood that my invention is not-limited to specific details oi construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An air circuit breaker comprising relatively movable contacts arranged to draw the interrupting'arc substantially simultaneously within two arc' extinguishing structures, one ofsaid structures having arc barriers composed of an inorganic insulating material arranged to lengthen and attenuate the arc as it passes into said structure so as to cool the arc stream and greatly increase its electrical resistance, the other of said extinguishing structures forming a pasinorganic insulating arc barriers arranged to lengthen and attenuate the am as it is driven by the blowout field into said structure so as to cool the arc stream and greatly increase its electrical resistance, the other of said extinguishing structures also comprising an arc chute forming a passage in which a portion of the interrupting arc is drawn, said passage having walls in part surrounding saidarc portion composed of insulating material adapted to release an appreciable volume of arc extinguishing gas under influence of the are heat, said last-named arc chute having venting means for directing said gas so as to extinguish said are portion by expulsive ac-- tion.

3-. An air circuit breaker comprising relatively movable contacts arranged to draw two interrupting arcs in series, an arc chute in which one of said arcs is drawn having magnetic blowout coils and interleaving arc barriers composed of an inorganic insulating material arranged to lengthen and attenuate the arc as it is driven by the blowout'field into said chute so ,as .to cool the. arc stream and greatly increase its electrical resistance, a second arc chute in which the other of said arcs is drawn for confining said arc, said second chute havin structure including spaced barriers in intimate relation to said arc composed of organic insulating material, such as hard fibre, adapted to release an appreciable volume of arc extinguishing gas under influence of the are heat,

said last-named arc chute having a plurality of venting passages for directing said gas so as to extinguish said are portion by expulsive action.

4. An air circuit interrupter comprising arcing means for the interrupting arc, an arc extinguishing chamber in which one part of said are may form havin closely confining walls of organic insulating material adapted to release an arc extinguishing gas under influence of the are heat and means for directing said gas from said to cool the arc and greatly increase its electrical resistance. 4

ROBERT M. 

